It is often desirable to be able to determine the proximity of a cellular or mobile telecommunications terminal to a particular point or location (a “special zone”). For example, some mobile or cellular telecommunications network operators wish to offer subscribers discounted call charges when their mobile terminals are located within a particular area—such as their home or place of work.
Various prior art arrangements for locating a mobile terminal have been proposed.
For example, it is known to use a mobile terminal to monitor the pattern of signals received from various cells of a mobile network and to record these values when the mobile terminal is in a particular location, this location being within the special zone. Subsequently, the mobile terminal measures the ambient radio signals from the cells and compares these with the recorded values. If the measured values are within a certain range of the recorded values, then the mobile terminal is deemed to be within the special zone. This can be signalled to the network in order to allow special calling rates within the zone. However, a problem with such arrangements is that a signal is received from the respective cells can vary significantly within a small area—for example, within a single house. Therefore, in order to ensure that the mobile terminal is deemed to be within this special zone when it is in fact in that zone, the range of differences permitted between the recorded values and the measured values has to be considerable. In practice, this means that the area within which the mobile terminal signals to the network that it is in the special zone is much larger than the special zone.
WO-A-00/01171 discloses an alternative arrangement. In this arrangement a device, which is intended to be located in a fixed position in the special zone, is provided with a short-range beacon, such as a Bluetooth beacon, which transmits a signal that is receivable by the mobile terminal when it is near to the beacon. Receipt of the signal from the beacon is transmitted by the mobile terminal to the mobile network in order that a special charging rate is applied. However, a problem with such systems is that the device containing the beacon can be moved, and the user of the mobile terminal will be able to receive calls at the reduced rate whenever the device containing the beacon is within range of the mobile terminal.
EP-A-1251711 discloses a system in which a device containing a short-range beacon which transmits the signal to a mobile terminal must be connected to a fixed socket, such as a mains power supply, for it to operate. With such an arrangement, it may still be possible for the user to re-locate the device containing the beacon and thereby obtain lower priced calls in an unauthorised manner. There is no way for the network to determine the location of the beacon.